Hip fractures occur in 280,000 Americans, over 5,000 per week. During the next 40 years, the number of hip fractures is likely to exceed 500,000 annually, and the estimated annual health care costs will reach a Staggering $9.8 billion. Hip fracture patients are at risk of a 30% mortality rate and impairment of independence and quality of life. Hip fractures are commonly treated with hip replacement, or arthroplasty. Two common types of arthroplasty exist, total hip arthroplasty (THA) and hemi-arthroplasty (HA). Advocates of hemi-arthroplasty (HA) focus upon reduced dislocation rates, lower rates of deep vein thrombosis, shorter operating times, less blood loss, and a technically less demanding procedure. Surgeons supporting THA perceive benefits in improving patient function and improving quality of life. Methodological limitations of previous studies, as well as their small sample sizes and resulting wide confidence intervals, have left the optimal operative approach unresolved. Objectives: In patients over 50 years who have sustained a displaced femoral neck fracture, what is the rate of re-operation at 2 years when THA versus HA is used as the surgical treatment? We will also evaluate patient function and quality of life. Study Design: To maximize the efficiency of our randomized patients, we propose an expansion of our ongoing pilot study into a vanguard phase of our proposed definitive randomized trial of 1, 316 patients, including 200 total patients in the US, who have sustained a displaced femoral neck fracture. This study will recruit 100 more patients across 12 US sites, and continue to follow the 100 patients from the pilot study. Patients will be randomized to either THA or HA and treated by surgeons with expertise in that technique. We will independently adjudicate revision surgery rates and collect functional outcome data at hospital discharge, 1 week, 10 weeks, 6-, 9-, 12-, 18- and 24-months. Hypothesis: We hypothesize that total hip arthroplasty will have similar or lower rates of re-operation (primary outcome) and higher functional outcome scores (secondary outcome) at 24 months compared with hemi-arthroplasty. This trial will not only change current orthopaedic practice, but will set a benchmark for the conduct of future orthopaedic trials.